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Helium Leak Testing

mass-spectrometersHelium Mass Spectrometers Detect Trace Gases

  • The HV Port opens to the vacuum and has the highest sensitivity.
  • The Sniffer Port opens to atmosphere and has a lower sensitivity.

Leak Tightness Checked with at Least 2 Configurations

gas-1Vacuum Inspection: Tests gas inside a part where the part is inside an expansive vacuum chamber, with vacuum under 0.02 psi absolute or 1 mBar absolute pressure. This known as “hard vacuum.” This is the most sensitive and recommended test method.

gas2Atmosphere Inspection (Accumulation): Tests gas inside a part where part inside an enclosure, but the enclosure is maintained at near barometric condition. This configuration, although simpler, is ~1000 less sensitive compared to the vacuum inspection.

Micro-Flow vs. Helium Mass Spectrometry (Chamber Test)

Function Mass Extraction Technology Helium Mass Spectrometry
Leak Flow Measurement Direct, accurate and independent of UUT volume Indirect, required frequent calibration and is volume sensitive
Gas Used Any gas, mostly air or nitrogen Helium
Max. Sensitivity 6×10-7 std. cc/sec. 1×10-10 std. cc/sec.
Vacuum Level (absolute pressure) at instrument 1 to 200 mm Hg (1-200 tor) 1×10-3 to 1×10-4 mm Hg (tor)
Drive, measurement stability Very Good (2-3%/year or better); Sensitive to UUT out-gassing Poor, sensitive to background helium level
Vacuum System Simple mechanical vacuum pump Sensitive hard vacuum system with diffusion or molecular pumps
Operation Simpler Complex
Operational Cost Very low Expensive – helium is an expensive gas, and becomes harder to get.
Maintenance Cost Very low, simple system Expensive, sensitive pumps and valves
Response Time Slow Slower at higher sensitivity

Helium Sniffer Detectors

Helium sniffers only find the point of leak, which are misleading. Helium sniffing is very operator dependent. Helium permeates through Teflon and other seals, creating false indications. Some companies will use these as line leak testers, which is incorrect.

Consult ATC, Inc. if you are looking to upgrade or replace your tracer gas leak test system.

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